Upgrades on gauges questions

Del said

I am replacing the amp guage with a volt guage can the same wires be used that were already being used

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No. The ammeter is an internally shunted meter in the battery feed/charging circuit.
See where its located in the diagram?

1960 Imperial and Chrysler Tech - Alternator Service page 8

The other gages operate through a voltage regulator when the ignition switch is in run.
1963 Electrical Diagnosis, Voltage Limiter & Gage Operation, p. 10. Master Technician's Service Conference